What is keratoconus?
Keratoconus (KC) is an eye condition in which the normally evenly curved dome-shaped clear lens at the front of the eye (the cornea) progressively thins. This causes a cone-shaped bulge to develop in the corneal tissue. Exactly why this happens is unknown, but genetic factors are known to play a role and KC is also more common in people with allergic diseases such as hayfever and asthma. We believe that the mechanical trauma from people with such problems rubbing their eyes plays a part in causing the cornea to thin. KC is usually diagnosed in teenagers and young people.
How does keratoconus affect vision?
The thinning of the cornea caused by KC changes its shape, altering its optical properties, and in later stages there may also be scarring which results in a loss of transparency of the cornea. These issues impair the ability of the eye to focus properly, resulting in impaired vision. Because the conical shape of the cornea is not symmetrical or regular it is difficult (and often impossible) to obtain good vision with spectacles.
Treatment for Keratoconus
In the early stages of KC spectacles or soft contact lenses may be helpful to correct vision and we treat associated problems like allergic conjunctivitis. As the cornea becomes thinner and the curvatures greater or steeper, rigid gas permeable (RGP) contact lenses are often required to correct vision more adequately. In very advanced cases, where contact lenses fail to improve vision, replacement of the cornea with tissue from an organ donor (a corneal transplant) may be needed.
The changes in the shape of the cornea caused by KC often take many years to develop. For this reason we monitor those with the condition and often suggest repeat assessments so that we can institute appropriate measures to optimise vision. We use the best spectacle correction and also objective measurements of the shape of the cornea using a special scan called a Pentacam to determine the severity of the disease and also to monitor its progression. If we see these results getting steadily worse we would discuss with you whether you need to undergo corneal cross-linking (CXL).
Corneal Cross-linking is a new treatment that can stop KC getting worse. It is effective in more than nine out of 10 patients and requires only a single 30-minute day-case procedure. The corneal tissue is soaked in Vitamin B2 (Riboflavin) and then exposed to ultraviolet light. This treatment strengthens bonds between the collagen fibrils which make up the main part of the cornea which we call the ‘stroma’. CXL is generally only used if the corneal shape is progressively deteriorating. There are limits to what treatment can achieve, and beyond a certain stage, particularly if the cornea has become too thin, it can be unsafe to perform CXL. Also by the time people reach their late 30’s the cornea naturally stiffens so CXL is generally not required. Below this age, the cornea is more flexible and disease progression, with the associated worsening vision, is more likely to occur.